The invention pertains to a apparatus for determining the position of the rotor of an electric machine in relation to the stator, wherein the machine comprises several phase strands, each of which comprises a pole winding with a magnetizable core, with devices for acquiring measurement signals characteristic of the instantaneous degrees of magnetization of the pole winding cores influenced by the rotational position of the magnetic field of the rotor.
An apparatus of this type is described in DE 10 2006 046 637 A1. The magnetic field of the rotor of the electric machine magnetizes the cores of the pole windings to different degrees as a function of the angular position of the rotor, resulting in different degrees of angular position-dependent magnetization and thus to different inductances in the phase strands. Over each half of a magnetic period there are unique relationships between the inductances and the angular position of the rotor. The angular position of the rotor can be determined by acquiring signals representative of these inductances.